Greyscale flat bed digital scanners are well known to the art. One such scanner using a charge coupled device (CCD) sensor is illustrated and described, for example, in U.S. Pat. No. 4,500,197. Such apparatus optically scans documents on which data is imprinted on reflective media. The documents are placed face down on a transparent top and are optically scanned by a scanner located within the apparatus under the transparent top. The resulting data is digitized in the prior art apparatus and computer processed for transmission, for example, over telephone lines.
The prior art flat bed digital scanners use light sensitive detectors to measure the reflected light level from the scanned document, such as a photograph, printed matter, magazine page, or the like. Such light sensitive detectors use a technology known as Charge Couple Device (CCD), and serve to quantitize the data in a format suitable for computer processing to be reproduced by peripheral equipment such as a monitor and/or printer, or to be transmitted to remote locations over the telephone lines by appropriate MODEMs.
As mentioned above, the prior art flat bed scanners operate in conjunction with reflective opaque media and the prior art scanners operate by directing an optical beam to the under surface of such media to be reflected by the data imprinted thereon.
The present invention provides an assembly which may be removably mounted on a prior art flat bed scanner to enable the scanner additionally to process data imprinted on transparent media, such as X-ray films. This concept enables inexpensive flat bed digital scanners to be used to scan and digitize data on X-ray films for local reproduction and/or for transmission to remote points.
It has been usual in the prior art to digitize X-ray films by relatively complex and expensive equipment. Such equipment uses photosensitive detectors and precision positioning mechanisms to provide a wide dynamic range of optical density (greyscale) and to maintain accurate spacial representation.
As mentioned above, the present invention enables low cost digitizing flat bed scanners to be used for the same purpose as the more expensive prior art equipment described in the preceding paragraph. As will be described, such low cost flat bed digital scanners may be constructed to perform transparency digitization and to provide an optical density dynamic range greater than the prior art CCD technology used in the more expensive prior art machines will allow.
The optical scanner utilized in the apparatus of the invention is a charge coupled device (CCD sensor) which is used in place of the more bulky conventional optics found in other prior art document scanners. The prior art has typically demonstrated the use of the combination of lens optics and mirrors in order to achieve translation of the image of an illuminated object placed on a document platen glass to an imaging station where the image is exposed into a sensitized photoconductor.
The application and use of the CCD sensor as a scanner provides a way to reduce dimensional space requirements taken up previously by prior art optical scanning apparatus, because of the relatively small size of the CCD sensor assembly. The means of reducing the scanner size is demonstrated in the system described in U.S. Pat. No. 4,500,197. The system of the invention, when combined with other new electronic technology, allows the image of the source material to be processed and developed in different efficient ways. For example, the resultant image may be converted into a train of electronic pulses which are reconstructed on the screen of a cathode-ray tube which may be remotely situated. The images may then be projected directly onto a photoconductor surface where conventional copier processes are used for image development and for transfer of the image onto copy paper.
A typical CCD scanner is partially comprised of a scanner assembly having an optical path with dual mirrors which are arranged compactly so that multiple reflections are generated between the two mirrors. There may be typically six reflections of an image between the two mirrors which necessitates maintaining a strict unyieldable structural relationship between the two mirrors. The need for a rigid vibration-free relationship between the CCD scanner and the mirrors becomes especially critical during translating motion of the scanner carriage.
A solution of certain problems relating to obtaining a direct illuminated image by adjusting the CCD lens unit to the cooperating, compactly arranged mirrors, without physically adjusting the mirrors has been demonstrated in the prior art. Avoidance of disturbing this particular mirror arrangement is highly desirable because of the inherent difficulty in aligning and rigidly holding mirrors designed and intended to generate multiple reflections. These difficulties are greatly compounded because of the mounting of the mirrors in a carriage which is slidably mounted on rails and supported in structure comprising the framework of a machine which has other mechanisms additionally mounted to such framework thereby causing various vibrations or shocks which could adversely affect the reproduction of an image.
An objective of the present invention is to enable a conventional prior art flat bed greyscale and color digitizing scanner to retain its normal feature of digitizing data imprinted on reflective medium by providing a mechanism that will allow the detector electronics of the scanner to recalibrate the mechanism for use in conjunction with X-ray transparencies and the like. It is the nature of the photosensitive detector charge coupled device (CCD) that each detector must be calibrated prior to use. This is due in part to the imperfect nature of the manufacturing process for each detector cell that contributes to an uncertain output.
To overcome the above-mentioned drawback, a common technique in the prior art is to stimulate the detectors prior to scanning with a different reference source. This reference source in the prior art reflective-type scanners is in the form of a white strip that uniformly reflects the excitation light to the detector electronics such that the CCD output can be measured. This measurement then becomes an equalizing reference and establishes the compensation value for the CCD array of detector cells during normal operation of the scanner in conjunction with reflective type media.
The present invention provides an additional reference strip which is used in a second mode of operation of the scanner during which it is processing data on transparent media, such as X-ray films, so as to calibrate the CCD array prior to scanning X-ray films or other transparencies.
Another objective of the invention is to provide a system for use in the conventional CCD detector based flat bed scanner to achieve greater optical density sensitivity dynamic range by improving the detector electronics so as to provide programmable photon integration periods. Such system provides dynamic control of the detector exposure time to enable the CCD to achieve a wider range of sensitivity and thereby significantly improve performance.